1. Field of the Invention
The present invention relates to an adaptive collision avoidance apparatus and a method in channel-hopping based wireless AD-HOC networks, and more particularly, to a technology capable of enabling smooth communications even in the case that the quality of channels is poor and reducing power wastage due to packet loss by preventing the channels having quality lower than a predetermined level from being used when the quality of channels are poor due to frequency selective fading or collision signals from other wireless devices, or the like, in channel-hopping based wireless AD-HOC networks.
2. Description of the Related Art
It is the case that most recently developed wireless communication devices for configuring wireless networks are operated in industrial, scientific and medical (ISM) bands due to the saturation of frequency bands and convenience of development and use. Further, the wireless communication devices used in these bands have become evermore diversified and the number of wireless communication devices used therein has been rapidly increased.
Meanwhile, as the representative related art for configuring low-power wireless networks, there are an IEEE 802.15.4 link and a physical layer technology. Basically, this technology configures the wireless networks using one channel. However, when there are different wireless devices in the use channels, the quality of communications is considerably reduced.
As a robust communication method resistant to the collision in the above-mentioned wireless band, there is a channel-hopping technology using a plurality of channels and performing communications while changing the channels according to the allocated channel hopping sequence. According to the technology, robustness is largely increased as compared to that in IEEE 802.15.4 technology, since communications can be performed in other channels, even in a period of congestion caused due to the existence of the collision devices in one or more channel. However, when attempting communications, even in poor quality channels, most communications fails due to collisions if there is not a separate apparatus managing the quality of channels. Therefore, the quality of communications is degraded and power is unnecessarily consumed. In the worst case, when attempting the communications in the poor quality of channel all the time, the communications link may be lost.
As for the related art to avoid collisions in channel-hopping based networks, there exists a Bluetooth adaptive frequency hopping (AFH) technology, a central concentration technology, and a technology of changing occupied time, and the like.
According to the Bluetooth AFH technology, the degradation in quality of communications is prevented by changing the frequency hopping sequence according to the channel environments. However, since this technology should transfer the hopping sequence to peripheral nodes, it is difficult to apply to general multi-hop networks other than a star network.
Further, according to the central concentration technology, one managing node that manages the networks measures the quality of channels to select the channels that are not used in the network and propagates them to the entire network. In this technology, it is assumed that the nodes configuring the entire networks suffer from the same or similar channel characteristics; however, when the actual scale of the network is large, the technology may not substantially meet this assumption, such that there is a problem in that there are unavailable channels, even when the real quality of channels is good. Further, the delay time to propagate the unavailable channel information to the entire network is long, as well as it is difficult to transfer the information to all the nodes. As a result, it is difficult to apply the central concentration technology to a real network.
The technology of changing the occupied time in each channel according to the quality of channels without changing the hopping sequence is also difficult to apply to a general multi-hop network other than a star network, since all the nodes in the network should share the occupied time for each channel